1. Field of the Invention
The present invention relates to wireless communication, and more particularly, to a method and apparatus for avoiding inter-cell interference in a multi-cell environment.
2. Description of the Related Art
In recent years, multiple input multiple output (MIMO) technology is primarily considered as one of technologies used in a next-generation mobile communication and wireless transmission system. The multiple input multiple output (MIMO) technology is a method for enhancing a spectral efficiency using multiple antennas to enhance a low spectral efficiency that has been a problem of the single input single output (SISO) method in the prior art.
The multiple input multiple output (MIMO) technology can be divided into a spatial multiplexing technique and a spatial diversity technique according to whether or not to transmit the same data.
The spatial multiplexing technique is a method for transmitting different data through several transmitting and receiving antennas at the same time. In other words, different data is transmitted through each transmitting antenna at the transmitter side, and suitable interference removal and signal processing is carried out for the received signals at the receiver side to obtain the transmitted data, thereby enhancing data transmission rate in proportion to the number of transmitting antennas.
The spatial diversity technique is a method for transmitting the same data through several transmitting antennas to obtain transmission diversity. In other words, the spatial diversity technique is a kind of space-time channel coding.
In such a spatial diversity technique, the same data is transmitted from several transmitting antennas, thereby greatly enhancing a transmission diversity gain. However, the spatial diversity technique is not a method for enhancing a transmission rate of data, but for enhancing the reliability of data transmission by enhancing a diversity gain.
Furthermore, the multiple input multiple output (MIMO) technology can be divided into an open loop method and a closed loop method according to whether information on channels is fed back from the receiver side to the transmitter side. Of them, the multiple input multiple output (MIMO) technology with a closed loop method may enhance a transmission rate of data using channel information fed back from the receiver side.
In other words, in case of a closed loop multiple input multiple output system, if transmission channel information has not been received from a terminal, then a base station may not know transmission channel information on a terminal being serviced. Accordingly, information on channels such as a channel quality indicator (CQI), a precoding matrix index (PMI), and the like is fed back from the terminal to the base station.
Currently, a lot of studies on a closed loop multiple input multiple output system are carried out, and the closed loop multiple input multiple output system is applied and used in a multi-cell environment as well as a single-cell environment. When a closed loop multiple input multiple output system is used in a multi-cell environment, each base station allocates a precoding matrix index (PMI) on the basis of an optimal codebook to a terminal based on a channel situation between the base station itself and each terminal to provide high-quality services to the terminal.
However, a terminal located at an edge of the cell may be interfered by a pre-codebook allocated to a terminal belonging to the adjacent cell by the base station of the adjacent cell because a signal from the base station of the cell to which the terminal itself belongs is weak. The terminal located at an edge of the cell may have a problem of deteriorating the performance thereof due to inter-cell interference.
A coordinated multi-point (CoMP) transmission method has been developed to reduce interference phenomenon between cells in a multi-cell environment. The coordinated multi-point (CoMP) transmission method has been developed to reduce inter-cell interference in a multi-cell environment and enhance the communication performance of the terminal located at an edge of the cell.
However, in case where a method of limiting the PMI of the adjacent cell is required to perform coordinated multi-point (CoMP) transmission, it should be determined which PMIs are to be limited when there exist a plurality of PMIs to be limited due to interference from several adjacent cells. At this time, there is a problem of causing an overhead in case where PMIs of all the adjacent cells are taken into consideration.
Accordingly, it is needed to solve to which cells the PMI limitation will be applied.